A urea solution or a urea-based solution is often used in automobiles to reduce exhaust emissions. For example, some diesel-powered motor vehicles include a urea tank separated from the fuel tank. The urea tank is used for carrying a working fluid such as an automotive urea solution. The automotive urea solution is stored in the urea tank and injected into the exhaust of a vehicle to convert nitrogen oxides into basic nitrogen and water, thereby reducing harmful emissions from the vehicle.
The overall implementation of the National Standard IV and higher emission standards requires that all heavy-duty commercial vehicles must be equipped with an SCR system or an equivalent emission after-treatment device. Most of existing automobile manufacturers prefer the SCR system and thus urea is necessary. Only when it is ensured that the automobile urea solution is in a certain concentration range, can the oxide be fully converted into nitrogen and water. The excessive of concentration will cause secondary pollution of NH3. The lack of concentration cannot ensure that the emission standards are met. The use of tap water or sea water out of fraud or the adding of other solvents such as diesel oil by mistake may even cause damages to the expensive after-treatment system. With the enforcement of an on-board diagnostics (OBD) system, if the emission standards are not met or the quality and concentration of urea does not meet the requirements, the torque of the vehicle is limited and even the vehicle cannot be started. Therefore, with the implementation of Euro VI standards, a quality sensor becomes a mandatory installation component. Based on the above situation, the precision of detecting the concentration of urea in a urea solution is very important.
A sensor for measuring a liquid is disclosed in the existing art.
The sensor includes: a light source operatively coupled to an inner chamber disposed in a liquid solution and configured to emit light and transmit the light to the inner chamber; a light detector operatively coupled to the inner chamber and configured to receive at least a portion of the light from the inner chamber; and a controller configured to determine a concentration or quality of the liquid solution on a basis of the light emitted by the light source and the portion of the light received by the light detector.
Although the above-mentioned sensor for measuring a liquid may measure the concentration of urea, factors affecting the testing precision in the urea concentration testing process cannot be eliminated. For example, bubbles in the solution to be tested cannot be eliminated in advance. If the solution to be tested is bubble-doped, the precision of testing the concentration of urea will be affected. Therefore, the result of testing the concentration of urea obtained has low reliability.